At the end of this module, students should be able to…
describe what is observed without trying to explain, both in words and by means of a picture of the experimental setup (Scientific Ability B5)
design a reliable experiment that tests the hypothesis (Scientific Ability C2)
make a reasonable judgment about a given hypothesis based on experimental data (Scientific Ability C8)
“We must be clear that when it comes to atoms, language can be used only as in poetry.”
quantum spin - a property of quantum particles that has many mathematical similarities to macroscopic spinning objects but also has unique quantum properties not observed in the macroscopic realm elementary particles - subatomic particles that make up all known matter and cannot be divided any further into constituent parts
The quantum spin of a particle is one of the few physical properties that uniquely identify an elementary particle (along with information like mass and electric charge). We have seen that quantum spin is quantized and allows atoms and subatomic particles to interact with an external magnetic field. In this module, we’ll explore more in depth the behavior of quantum spins in a magnetic field in order to build up a classical analog of quantum spin that will be useful in making sense of the physics behind magnetic resonance in later modules.
For the activities below, we will be making use of an apparatus that provides a physical model of a quantum spin that has been designed to have many of the same dynamical behavior as real quantum spins, despite being a very classical, macroscopic object. Using this apparatus, we will explore important physical aspects of quantum spin and its behavior in an external magnetic field.
Gyroscope precession. Lucas Vieira, Public domain, via Wikimedia Commons.
Let’s observe the behavior of a gyroscope (essentially a fancy version of a toy top) that is first set on its point without spinning and then started off on its point with spinning. We want to write down everything we observe in both cases and try not to write comments or explanations for what is observed. We are going to develop our model of spin from the ground up, and try our best not to introduce any prior knowledge or assumptions that do not come directly from our observations.